View full sizeThe National Weather Service earlier this afternoon released this radar image showing the potential for severe weather moving into the Mid-Atlantic. The area under a tornado watch, in red, has since been expanded to include parts of New Jersey and Pennsylvania.Image courtesy National Weather Service

Tornado watches have been lifted for Hunterdon County and southeastern Pennsylvania, including Bucks County, the National Weather Service said.

The Lehigh Valley and northwestern New Jersey were under a dense fog advisory that expired at 3 this afternoon, the weather service also said.

The tornado watch put in place at 12:40 p.m. has been lifted in Pennsylvania's Bucks, Chester, Delaware, Montgomery and Philadelphia counties. The New Jersey counties still under a watch through 5 p.m. are Atlantic, Burlington, Camden, Cape May, Cumberland, Gloucester, Mercer, Middlesex, Monmouth, Ocean, Salem and Somerset counties.

"The threat of severe weather has significantly escalated for this afternoon," weather service meteorologist Gary Szatkowski said in an email to emergency managers earlier this afternoon.

Locally, visibility was forecast to be limited to a quarter-mile or less, though the fog was expected to lift with the possibility of both warm and cold fronts moving through the area, the weather service said in the dense fog advisory.

Drivers were urged to slow down, use low-beam headlights "and leave plenty of distance ahead of you in case a sudden stop is needed," according to the advisory.

Rain showers, with some thunder, were forecast early this afternoon, with total precipitation in the range of a quarter-inch -- possibly more in heavier showers; the weather service said; wind gusts of up to 30 mph were possible in thunderstorms.